High-frequency energy transfer circuit



March 11, 1952 c. w, HANSELL.

HIGH-FREQUENCY ENERGY TRANSFER CIRCUIT Filed Nov. 20, 1947 A INVENTOR CLARE E W. HANSELL BY i l I AT QRNEY NN NNNNNNNNN\ lill] 11111111111111111111 4 Patented Mar. 1l, 1952 HIGH-FREQUENCY ENERGY TRANSFER CIRCUIT Clarence W. HanselLPort Jefferson, N. Y., assignor to Radio Corporationpf.America,.a Ycorporation ofDelaware Application November 20, 1947,4 Serial No.l787',233

,2.7 Claims. l This invention'relates to a'novel method of and meansfor ltransferring radio frequency 'power fromone transmission line .to another.

Among the objects of the invention are,zin Vcir.

cuitsfor the-.transfer of radiofrequency energy between a pair of coiled transmissionlines: lto avoid the occurrence of backward 4travelling waves; :and `to increase the frequency selectivity at which vtotal radio frequency energy transfer fromone'line Vto the other occurs.

Briefly stated, the present invention comprises an energy transfer circuit'for 'radio frequency power, in the form of two similar coiled transmission lines which are arranged parallel to but spaced from each other and coupled electrically for a distance chosen such that transfer of energy therebetween is substantially complete at a particular frequency. The two coiled lines arepreferably though notnecessarily similarly dimensioned in diameter and pitch. In order tovassure complete energy transfer between the two coiled lines, theiraxial wave or phase velocities should be equal, but the characteristic impedance of the coiled lines need not be alike. The coils are properly spaced and unshielded from one another for a suitable distance to effect the desired degree of energy transfer therebetween, and preferably they are so terminated that waves transferred from one coil to the other travel inthe last coil in the samedirection as the waves'in the .jrst coil, with negligible backward traveling waves. Thespacing between coils is .adjusted to a correct value to cause acomplete transfer of Venergy within those portions of thelengths of the coiled lines which arecoupled together, and this may I be achieved by trial while watching meter readings of the currents along the lines. kThe back- Ward traveling waves .are caused by reflections after thecouplingiseffected and these may be controlled to be verylsmallforfappreciable, as-desited. Onemanner of `reducing these y'reflected waves to prevent vrereilectiom'forward again in thedirection of ther'original waves, is'to `provide high .attenuation ends for the coils,'as for example, by coatingsthe'ends ofthe coils with a layer of colloidal graphite sold underrthe trade name Aquadag. However anyother means for givin-g the ends ofthe lines a high attenuation may. .be.used.

VAmore complete :description of the invention follows. The foregoing ,and1otherobjects, advantages-and novel Lfeaturesoffthe invention will be more jfully :apparent from :this description when. read in,.conjunction-with.a drawing whose single ngure :illustrates eone embodiment if the invention given-by wayof example only.

Yltezferring-to the drawing, there are shown two coiled transmission lines Afand B correctly 7spaced from but coupled tofeach other by substantially continuous yreactive .coupling therebetween. Coiled line A may be consideredas the primary coil since input -waves are applied 'to one :end

thereof -by anyv suitable source of veryhighfrequency waves.

The 'source of vinput waves'is here shown,by way f of example only, as Aa growing wave v(isometimes calledI a traveling wave) 'typetubecllL illustrated dia'grammatically. 'The input end of coil A isshown as the continuation of the helix 'within l,the tube-Illand to which the electron stream is coupled. As is known,.thisgrowingwave tube Ama-gnetic eldv--coil-,serves to-focus the-electronstreamfalong-orparallel to the longitudinalfaxis of the tube. Fora general 'description of the operation of such lgrowing wave ltubes reference is vherein made to VvLindenblad Patent 2,300,052, granted October 27,1942, and to my copending application Serial No. 787,232, filed Novembert20, 1947.

ing axially-along Ythe length of primary coil -A there is-provided` at endE of Ythe coil A, a region offfliigh waveA attenuation, which may beobtained byf-:applyingpalayer of `riquadag. :Statedaotherfwise; the 'end `E remote from "the input end ,of-.the coil A is a lossy'end-which valmost completelydissipates or absorbs power-from the waves :reaching theend.

.Coiled' line. B may lbe considered as ther second- .ary coilwhich by'proper exposure `and spacingA from coil A obtainsa substantially continuous .reactive coupling for a complete transfer of .energy of a-;.selecte d.frequency .or band of .frequencies from V,coil 5A, with ya wave traveling along ycoil VB 'nthesame direction as -thewave traveling ,along coil A. One endE of coil B is coated withalayer of Aquadajgfcr otherwiseggiven high attenuation,

in thegsame' manner as end =E of .coil A., in.orde1 DIOVde 2.a high attenuation termination @and prevent 'wave .reflections at .this end. The i other I In order to preventv reflections of waves'travelend of coil B is tapered in diameter and pitch (decreasing diameter and increasing pitch) so as to gradually reduce the characteristic impedance of this end to a characteristic impedance of the order of 50 to 75Y ohms while the characteristic impedance of coils A and B at their exposed portions may be as great as several hundred ohms or more.

In order to shield the lossy or high attenuation end E of the coiled line A from the adjacent portion of the line B, and to shield the lossy end E of the coiled end B from the adjacent portion f line A, there are provided, metallic partitions P and P', respectively, which prevent useful energy of the waves traveling in a forward direction in the coiled lines A and B from getting into these lossy portions.

The magnitude of the current in coiled line A will be a maximum near the input end and gradually fall off to a minimum near thelossy end E. Similarly, the magnitude of the current in coiled line B will b`e a minimum neary the lossy end E l and amaximum near the end coupled to the utilization circuit or coaxial output line 20. This condition will exist for correctI spacing between coiled lines A and B for complete energy transfer therebetween.

Axial velocities/of waves along both coiled lines (each talen alone) should be equal for complete energy transfer, although the characteristic impedancesof both coiled lines need not be alike. The spacing and/or length of exposure between the two lines is adjusted to a correct value to cause a complete transfer of energy within those portions of the lengths of the coiled lines which are coupled together. This is eifected by trial while watching meter readings of the currents along the lines, although, once correct relationships have been determined they may be duplicated in construction.

This complete energy transfer will take place at a particular optimum frequency. At frequencies far removed from this particular frequency, the net energy transferred from one coiled line A to the other B will not be complete.

At frequencies much higherthan the optimum for complete net transfer of energy, it will be found that the energy in the primary coiled line A first transfers itself completely to the secondary coiled line B but before the end of the coupling region is reached much of the energy of the transferred waves will be returned again to the primary line A. At frequencies much lower than the optimum, there will be incomplete transfer of energy; or putting it in other words, the coupling region will be too short for complete energy transfer. Thus there is frequency selectivityover a broad band of frequencies. This arrangement may be used to transfer nearly all the energy within a band of frequencies having a range of the order of less than 2 to 1.

When increased frequency selectivity is desired, the lines may be given different dimensions of diameter, pitch and dielectric constant of the support, resulting in different impedances and a different rate of change of phase velocities with frequency, provided the velocities still match at the desired range of frequencies. Then the velocities become unequal at other frequencies, which diminishes energy transfer at these other frequencies.

As a refinement, it may be advisable to have a tapered coupling between the two coiled lines A and B by having the coils slightly diverge from each other along their lengths, so as to minimize small reflections which may otherwise take place at the ends of the coupling regions.

The coupled regions of the two coiled lines A and B may be 15 wavelengths more or less at the mean operating frequency, the wavelength being measured along the coil, not at the velocity of light. Coiled lines A and B are shown mounted within an outer shielded metallic envelope to prevent wave energy transfer to and from nearby surfaces and objects.

The frequencies used in the transfer of energy from one coil to the other may range anywhere from 500 megacycles up to thousands of megacycles.

Although I have described the coupling as applied to the output end of a growing wave amplifier, it should be understood that the same arrangement may serve for coupling to the input end of the amplifier merely by reversing the direction of the waves through the system.

An advantage of this frequency selective energy transfer system is that the waves not transferred are to a very large degree absorbed in the lossy portions of the lines so that to and fro wave reflections cannot take place to any substantial degree at any frequency. In the growing wave amplifier application, this feature is very helpful in preventing uncontrolled oscillation of the amplier of a kind usually referred to as parasitic oscillations.

What is claimed is:

l. The combination with a radio frequency energy transfer circuit comprising a coiled line a plurality of wavelengths long at the operating frequency of the waves adapted to travel thereover in an axial direction, a portion of said coiled line solely near one end being constructed and arranged to provide high attenuation for said waves passing over said line, of means for supplying high radio frequency waves to said coiled line at a location removed from said one end to travel in said direction toward the other end comprising a second coiled line coupled to said first with substantially continuous reactive coupling over a plurality of wavelengths at the operating frequency, and means remote from said one end abstracting high frequency waves from said first line.

2. The combination with an energy transfer circuit comprising a coiled line a plurality of wavelengths long at the frequency of the waves adapted to travel thereover in an axial direction,

a coating of material on solely one end of said' coiled line, said coating comprising a layer of a material which provides high attenuation foisaid waves, of means for supplying high frequency waves to said coiled line at a loca-tion removed from said one end, and means for abstracting high frequency waves from said line from another location removed from one end.-

3. A coiled transmission line a plurality of wavelengths long at the mean operating frequency of the waves adapted to pass thereover, the turns of said line located solely near one end being constructed and arranged to provide high attenuation for said waves passing along said line in order to reduce wave reflections from said one end, the other end of said line being tapered in diameter and pitch for/association with a utilization circuit.

4. A coiled transmission line a plurality of wavelengths long at the mean voperating frequency of the waves adapted to pass thereover,

a portion of said line solely near one end being coated with a material which provides high at-v..

tenuation forfrsaid waves-.traveling over :'sad., line to reduce reflections from rsaid Aone fend, .the other end :of said vline :decreasing y,gradually in diameterzand increasing in Vpitch for reducing the Aterminal .characteristic impedance rof vsaid line.

5. Anenergy :transfer circuit betweena source of highfrequencywaves iand a utilization circuit, comprising fa A.coiled transmission line va plurality of wavelengths Vlong at the-mean operating frequency :of nthe Awaves adapted to :pass over said line, one fend of said line-being coupled to said source and means coating saidsline solely near the :other fend-with'a .material which provides :a high vattenuationfor the waves reaching saidlast end, whereby rwavereflectionsrfrom sai-d last lend are minimized.

6. An energy :transfer Acircuit for Aradio frequencypower comprising a pair'ofrspacedsubstantially iparall-el'ly arranged coiledptransmission lines each a plurality :of v.'vvavelengthslong nat-ptlie mean operating frequency andin ienergy coupling lrelation Ato each other solely :byfvirtue 'of the .spacing therebetween overpadistance equal to ia plurality of wavelengths long, :said lines being so dimensioned :and 'arranged that fthe axial velocities of the waves at a selected ifrequency along 'bothlines aresubstantially equal, a portion ofionecoiledzline.located solely near one end and a portion ofthe'otherfcoiled line located solely near the opposite end being so constructed and'arranged as to provide high attenuation for the'waves traveling over the respective lines, the spacing land length of electrical exposure betweensaid lines being-so chosen as to effect a substantially `completetransfer of energy between Ysaid 'coiled lines rat* said selected frequency.

'7. An energy transfer circuit for radio -frequency power comprising 'a `primary coiled transmission line a plurality of wavelengths long at the mean 'operating-'frequency'a secondary coiled transmission line also a plurality of wavelengths long at the mean operating'frequency'and having Va portion arranged substantially parallel and adjacent to aportionof said first line so as Ato be 'inenergyicoupling'relation thereto solely Vby virtue of the'spacing :therebetween, the coupledportions 'ofboth lines being longer than several 'wavelengths at 'the Vmean operating frequency, means for supplying radio frequency power to one Vend of 'said primary coiled line, means for deriving wradio frequency power from the `opposite end of said secondary coiled line, thespacing betweenthe coupled portions of said lines being-so'chosen as to effect Va substantially ycomplete transfer of 'energy between said coiled lines atsaid operating frequency, said lines .being so dimensioned-and :varranged that theaxial velocities-.of waves at :said frequency traveling along both lines are substantially equal, said `coiled lines `have portions located vsolelyat-theotlfler Vends soconstructed and arranged .as-to provide high yattenuation for rthe YWaves traveling .over therespective lines toreduce .wave reflections.

8. An energy transfer circuit forradio vfrequency .power -comprising a primary Ycoiled transmission line a plurality of wavelengths long at the mean operating frequency, a :secondary coiled transmission line also a .plurality .of .wavelengths long at the meanoperating.frequency and having a portion arrangedsubstantially parallel and adjacent to a portion of rsaidprimary coiledline so as to be in energy coupling relation thereto,solelyfbyvirtueof the spacing {therebetween, the coupled portions 4ofbothlines being longer than several wavelengths at Vthe mean operating frequency, means :for supplying .radio l frequency power to one end of said primary coiled line, means for deriving radio frequency power from theopposite Aend of said .secondary coiled line, the 'spacing between the Acoupled portions of saidlines-'being so chosen as toeffect'a substantially complete .transfer of energy between said coiled lines at said chosen frequency, said'lines being so dimensioned 'and arranged that the'axial velocities of waves at said frequency traveling along both lines are substantially equal, a vcoating of material at substantially solely the otherendsiofsaidlines, said coating material. providing high attenuation for the waves traveling over-'the respective lines, to thereby minimize reflections from said last ends.

9. .An energy transfer circuitfor radio frequency power comprising'aprimary coiled-,trans-` mission line a plurality-of wavelengths long iat the mean operating frequency, a lsecondary coiled transmission line alsoa lplurality of wavelengths long at the mean operating frequency and having a portion arranged substantially parallel andadjacent to'butspacedvfrom a portion of said primary coiled line so as .to bein energy coupling relation theretosolely by virtue of the spacing therebetween, the coupled portions of both lines being longer than several wavelengths at the mean operating frequency, means for supplying radio frequency vpower to one end of said primary coiled line, means for deriving radio frequency power from the opposite end of said secondary lcoiled linegthe spacing between the coupled portions of said lines being so chosen as to effect a substantially complete transfer of energy between said coiled lines at said operating frequency, said lines being Iso dimensioned andarranged that the axial velocities of waves traveling along both lines are'substantially equal, Ia coating Yof rmaterial at substantially solely the other ends of saidlines, said coating material providing high attenuation for the waves traveling over the respective lines, to

thereby minimize reflections from 'said last ends, and a shield-between each of said last ends and the adjacent coiled line,

l0. An energy'transfer circuitfor radio fre- -quency power comprising a primary 'coiled transmission line a plurality of wavelengths long at the mean operating frequency, -a secondary coiled transmission line-*also a pluralityof wavelengths long at the 'mean operating v.frequency and havinga portion spaced Vvfrom andarrangedv substantially parallel andadjacent to a portion of said primary coiled line so as to be in energy coupling relation thereto lsolelyby virtue of the spacing therebetween, the coupled portions of both lines'being longer thanseveral wavelengths at the mean operating frequency, -means for supplying radio frequency power to one end of said primary coiled line, means for deriving radio -frequencypower from rthe opposite end of said secondary coiled line, said last end of said secondary coiled line being vtapered in.diameter and pitch to reduce the .terminal characteristic impedance .of said ksecondary coiled line, the spacing between the lcoupledrportions of `said lines being so chosen as to effectA a substantially complete ,transfer of 1energy between said` coiledllnes at said operating frequency, .saidlines being so dimensioned and arrangedthat .the Vaxial velocities .of `waves traveling .alongbothflines are 2subaccesar stantially equal at said operating frequency, the`4 other ends of said coiled lines being constructed to provide high attenuation for the waves traveling over the respective lines to reduce wave relections.

11-. The method of transferring energy between a pair of coiled transmission lines each a plurality of wavelengths long at the mean operating frequency, which includes paralleling said transmission lines in spaced relation for a distance at least equal to several wavelengths long so that they are in energy coupling relation to each other by virtue solely of the spacing therebetween, feeding one end of one of said lines with high frequency energy, abstracting energy from the opposite end of the other line, providing high attenuation terminations at the other ends of said coiled lines, dimensioning said` lines such that the axial velocities of the waves along both coiled lines are equal, and so spacing said coiled lines from each other that there is a substantially complete transfer of energy from the line fed with high frequency energy to the line from which energy is abstracted at a desired band of frequencies.

12. The combination with an energy transfer circuit comprising a coiled line a plurality of wavelengths long at the frequency of the Waves adapted to travel thereover in an axial direction, a portion of said coiled line solely near one end being constructed and arranged to provide high attenuation for said waves passing over said line, of means for supplying high frequency waves to said coiled line at a location removed from said one end, and means for inductively abstracting high frequency waves from a continuous portion of said line intermediate the ends thereof and which portion isa plurality of wavelengths long.

13. An energy transfer circuit for radio frequency power comprising a primary coiled transmission line a plurality of wavelengths long at the mean operating frequency, a secondary coiled transmission line also a plurality of wavelengths long at the mean operating frequency and having a portion arranged substantially parallel and adjacent to a portion of said primary line so as to be in energy coupling relation thereto solely by virtue of the spacing therebetween, the coupled portions of both lines being longer than several wavelengths at the mean operating frequency, means for supplying radio frequency power to one end of said pri'- mary coiled line, said means comprising an electron discharge device having as part thereof a coiled line extending therefrom and forming an integral part of said primary coiled line, means for deriving radio frequency power from the opposite end of said secondary coiled line.- the spacing between the coupled portions of said lines being so chosen as to effect a substantially complete transfer of energy between said coiled lines at said operating frequency, said lines being so dimensioned and arranged that the axial velocities of waves traveling along both lines are substantially equal at said operating frequency, said coiled lines having portions located solely at the other ends so constructed and arranged as to provide high attenuation for the waves traveling over the respective lines to reduce wave reections.

i4. A frequency selective wave coupling system comprising two wave guiding systems of different dimensions having equal phase velocities at a selected operating frequency and` substantially continuous mutual reactive coupling ately less wave energy is transferred from oneA system to the other.

l5. Two wave guiding systems of different dimensions each terminated to prevent substantial wave reflections and having phase velocities' which are alike at a selected frequency but which differ due to the different dimensions by an increasing ratio as the frequency departs from the selected frequency, the two wave guiding systems being mutually coupled together with a substantially continuous reactive coupling to a degree and over a selected length which results in substantially complete transfer of waves originally in one of `the`systems over to theA other system only at or close to the selected operating frequency.

i6. Two wave guiding systems of different dimensions each terminated to prevent substantial wave reflections and having phase velocities which are alike for a selected operating frequency but progressively different due tothe differing dimensions for frequencies progressively further from the selected operating frequency, the two systems being substantially continuously and reactively coupled together` over a length or distance such that waves of the selected frequency entering one of the systems are transferred by the mutual coupling back and forth from one system to the other finally appearing nearly completely in the other of the two systems while waves of frequenciesY different from the selected frequency are less completely transferred.

17. A directional coupler comprising a pair of transmission lines of different dimensions having a substantially continuous reactive coupling over a length thereof at least a plurality of wavelengths at the operating frequency to provide substantially complete transfer of electromagnetic energy at the operating frequency, said transmission lines having substantially the same phase velocity for said energy at said operating frequency and each having a different rate of change of phase velocity with respect to frequency than the other due to different dimensions whereby the said energy is transferred with a band-pass effect.

18. A directional coupler comprising a pair of transmission lines each comprising a coil wound about a longitudinal axis and coupled by substantially continuous reactive coupling along an axial length of each at least a plurality of wavelengths at the operating frequency by `being placed in close proximity to each other with said axes substantially parallel over said lengths, said lines over said lengths having different dimensions and having substantially the same phase velocities for electromagnetic energy at the operating frequency and having phase velocities different from each other due to different dimensions for electromagnetic energy at frequencies other than the operating frequency the said lengths being that required for substantially complete energy transference from one' said line to the other at said operating frequency, whereby a band-pass effect is obtained in the coupling of energy from one said line to the other.

19. The combination with a traveling wave tube having a helical transmission line a plurality of wavelengths long at the frequency of the waves adapted to travel thereover in an axial direction, of another helical transmission line also a plurality of wavelengths long having a portion extending parallel to said rst helical line and in energy transfer relation thereto by substantially continuous reactive coupling therebetween, said lines having different dimensions of diameter and a different rate of change of phase velocities with frequency over a range of frequencies departing from the operating range of frequencies.

20. A combination as dened in claim 19, characterized in this that said helical transmission lines have a diiferent pitch.

21. The combination claimed in claim 18, said coil axes being parallel and spaced from each other.

22. The combination claimed in claim 18, said coil axes being parallel and spaced from each other, the said coils being positioned side-byside.

23. A directional coupler arrangement comprising iirst and second transmission lines each having a coiled conductor portion at least a plurality of wavelengths at the operating frequency over the length of Which there is a substantially continuous reactive coupling with that of the other, said lines having the same phase velocity over said length at the operating frequency, and each having on opposite sides of said coupling and removed therefrom one end portion decoupled from any portion of the other line except through the coupled line portions, means to apply electromagnetic energy to said one end portion of one line alone, the length of said coupling being that required for substantially complete transfer of energy at the operating fre quency incident from said one end portion to the other said line and travelling in one direction along said other line, whereby the energy transfer is complete at the operating frequency and less complete at other frequencies removed from the operating frequency, the said one end portion of the other said line being on the other side of said coupling, and means for withdrawing the transferred energy.

24. The arrangement claimed in claim 23, said transmission lines over said coupling portion having in atleast one respect differing dimensions whereby the frequency selectivity of the transferred energy is increased.

25. The arrangement claimed in claim 23, one coil having differing dimensions from the other over said length.

26. The arrangement claimed in claim 23, each said coil being helical, the helix axis of one being parallel to that of the other over said length.

27. The arrangement claimed in claim 23, each said coiled portion having axes parallel to and spaced from the axis of the other over said length.

CLARENCE W. HANSELL.

REFERENCES CITED The following references are of record in the lle of this patent:

UNITED STATES PATENTS Number Name Date 1,854,448 Cohen Apr. 19, 1932 2,115,826 Norton May 3, 1938 2,124,212 Rust July 19, 1938 2,159,648 Alford May 23, 1939 2,262,134 Brown Nov. 11, 1941 2,322,773 Peters June 29, 1943 2,423,390 Korman July 1, 1947 2,423,526 Sontheimer et al. July 8, 1947 

